The present invention relates to an inflator for generating gas for inflating and deploying an airbag and a method of manufacturing the same. More particularly, the present invention relates to an airbag inflator and a method of manufacturing the same having advantages such as reduced manufacturing cost.
Airbag inflators are gas generators for deployment of airbags. Some inflators have a plurality of gas combustion chambers. By adjusting the ignition selectively or ignition timing of the gas generants in the combustion chambers, the gas generation for deploying an airbag can be adapted to the severity of accident and the situation of an occupant, thereby achieving a preferable airbag deployment.
For instance, an inflator of this kind is disclosed in Japanese Patent Publication (KOKAI) H10-329638.
FIG. 5 is a sectional view showing the internal constitution of an airbag module. The airbag module shown in FIG. 5 comprises a gas generator (inflator) 104, and an airbag 102 which is deployed with a gas discharged from the gas generator 104. The inflator 104 is accommodated in a module casing 103. In FIG. 5, the airbag 102 is in a folded state. Defined between the inner surface of the module casing 103 and the outer surface of the gas generator 104 is a space S1 as a gas passage for airbag deployment.
The gas generator 104 comprises a cylindrical outer shell 121. Both ends of the outer shell 121 are closed by lid members 129A (left side) and 129B (right side). A disc-like partition 122 is fixed to a middle portion of the outer shell 121. The partition 122 comprises a central disc portion 122a and a flange 122b radially extending from the central disc portion 122a. The partition 122 is crimped at a drawn portion (crimped portion) 131 of the outer shell 121. The inside of the outer shell 121 is divided into a first combustion chamber GI with a small capacity and a second combustion chamber G2 with a large capacity. The id outer shell 121 is provided with a plurality of gas outlets 128a corresponding to the combustion chambers G1, G2. The gas outlets 128a are normally closed by burst plates 133.
Arranged in the combustion chambers G1, G2 of the outer shell 121 are filter cylinders 115A, 115B, respectively. Each filter cylinder 115A, 115B is composed of an inner shell 125 and a filter 124 attached to the inner surface of the inner shell 125. There is a space S2 as a gas passage defined between the inner surface of the outer shell 121 and the outer surface of the filter cylinder 115A or 115B. The inner spaces of the filter cylinders 115A, 115B are filled with gas generants 123. The inner shell 125 is provided with a plurality of gas holes 125a for allowing the communication between the filter 124 and the space S2. The left end of the filter cylinder 115A in FIG. 5 is fitted to a convexity 129a formed on the inner face of the lid member 129A. On the other hand, the right end of the filter cylinder 115B in FIG. 5 is fitted to a convexity 129b formed on the inner face of the lid member 129B. The flange 122b of the partition 122 is sandwiched between the filter cylinders 115A and 115B.
Annular seals 132 are interposed between the filter cylinders 115A, 115B and the flange 122b of the partition 122, respectively. The annular seals 132 isolate the gas flow and heat transfer between the filter cylinders 115A and 115B.
Cushion members 134 are attached to both surfaces of the central disc portion 122a, respectively. The cushion members 134 prevent the gas generants 123 to become powder and also isolate the heat transfer between the combustion chambers G1 and G2. The annular seals 132 and the cushion members 134 are made of a material having heat insulation property.
The lid members 129A, 129B at both sides of the outer shell 121 include initiators 126A, 126B. Each initiator 126A or 126B includes a booster propellant 135 and an igniter 136. The booster propellant 135 is accommodated in a cap 137 fitted to the convexity 129a (129b) of the lid member 129A (129B). As the igniter 136 is triggered, the booster propellant 135 is fired so that fire spouts out into the combustion chamber through holes (not shown) of the cap 137. The fire spreads to ignite the gas generant 123 so that the gas generant 123 burns to generate gas with high temperature and high pressure. The gas flows into the filter 124 where the slag contained in the gas is removed and the gas is cooled. Then, the gas flows into the space S2 through the gas holes 125a of the inner shell 125. As the inner pressure of the combustion chamber reaches a predetermined value, the burst plates 133 are torn, so that the gas spouts out into the space S1 through the gas outlets 128a. Then, the gas flows into the airbag 102, thereby inflating and developing the airbag.
Because of the two chambers G1, G2 of the gas generator 104, the deployment of the airbag 102 can be controlled as explained below.
In the highly severe collision, both initiators 126A and 126B are triggered simultaneously. Therefore, the gas generants 123 in the first and second combustion chambers G1 and G2 are fired simultaneously to discharge a large amount of gas, thereby inflating and deploying the airbag 102 immediately.
In the medium collision, the initiator 126B for the second combustion chamber G2 having a larger capacity for generating a larger amount of gas is triggered first. After a very short time, the initiator 126A for the first combustion chamber G1 having a smaller capacity for generating a smaller amount of gas is In triggered. Therefore, the airbag 102 is inflated and developed slowly by the gas generated in the second combustion chamber G2 in the initial stage. From the middle stage, the airbag 102 is developed rapidly by the total of the gases generated in both combustion chambers G1 and G2, respectively.
In the relatively light collision, only the initiator 126B for the second combustion chamber G2 is triggered. Alternatively, the initiator 126A of the first combustion chamber G1 is also triggered after a large time delay following the beginning of the initiator 126B. In this case, the airbag 102 is slowly inflated and developed for a relatively long period of time.
By the way, the conventional gas generator 104 mentioned above has the following drawbacks. When the gas generant 123 in one of the combustion chambers G1, G2 is fired, a large pressure difference is applied to the partition 122. Since the partition 122 is just crimped at the crimp portion of the outer shell 121, the sealing property between the chambers G1 and G2 is poor, though the thickness of the partition 122 is large.
To improve the sealing property between the chambers, as shown in FIGS. 6(A)-6(C), other crimping methods are also known in which sealing members, such as O rings and gaskets, are interposed between the outer periphery of the partition and the inner surface of the outer shell.
FIGS. 6(A)-6(C) are sectional views for explaining the examples of the fixing and sealing structure between the partition and the outer shell in the conventional gas generator.
Referring to FIG. 6(A), a gasket 155 is interposed between the outer periphery of the partition 152 and the inner surface of the outer shell 151, so that the partition 152 is crimped at a middle portion 152x in the thick direction of the partition.
Referring to FIG. 6(B), the partition 162 is provided with an O-ring groove 162x formed in a middle portion in the thick direction of the partition 162. An O-ring 165 is fitted in the O-ring groove 162x. The partition 162 is crimped at the portion where the O-ring 165 is fitted.
Referring to FIG. 6(C), this example is similar to the example shown in FIG. 6(B) using an O-ring 165 for sealing the partition 162. In this case, the partition 162 is crimped at two locations i.e. both sides.
Since the above examples shown in FIGS. 6(A)-6(C) use sealing members, such as the gasket 155 and the O-ring 165, however, the sealing member may be decomposed due to heat of combustion of the propellants in the gas generator, and mixed into the gas for deploying the bag. There is also a possibility of leakage at the sealing member due to hot blast produced when the propellants are burned. In case that the partition is formed with the O-ring groove 162x as shown in FIGS. 6(B) and 6(C), the thickness of the partition should be increased for ensuring the groove width. This increases the working cost and thus the manufacturing cost, and prevents the miniaturization of the gas generator.
Further, as another example, a gas generator is disclosed in Japanese Patent Publication (KOKAI) No. 2000-233705 published on Aug. 29, 2000, which was filed by the assignee of the present invention.
FIG. 7 is a sectional view showing the gas generator disclosed in the above application. As for the gas generator, description will be made as regard to only a partition (bulkhead) and an outer shell (housing). Description of the rest of the parts, i.e. initiator, gas generant, filter, will be omitted.
The outer shell or housing 201 of the gas generator is a cylindrical member. Disposed inside the housing 201 is a partition 203 having a substantially disc-like configuration. The partition 203 has enlarged edge portion 205 along the outer periphery thereof. The enlarged edge portion 205 has a width gradually increased toward the outer periphery so that its section is triangle.
The partition 203 is fixed to the housing 201 in the following method. Namely, the partition 203 is brought to a predetermined position in the housing 201, and tools, such as punches, (not shown) are inserted from the both sides of the housing 201. The tools are tapered toward the ends. The both surfaces of the partition 203 are pressed by the ends of the tools so as to plastically deform the outer peripheral portion of the partition 203 in such a manner as to bring the outer periphery of the partition 203 in close contact with the inner surface of the housing 201. This method for fixing the partition of the gas generator shown in FIG. 7 is advantageous. However, the thickness of the partition should be increased to withstand high inner pressure. The increased thickness makes the workability for fixing the partition 203 poor. Since the thickness of the enlarged edge portion 205 around the outer periphery of the partition should be correspondingly increased, it is difficult to employ the crimping of the outer shell 201 together.
There is another method disclosed in Japanese Patent Publication (KOKAI) No. H11-263185, which comprises preparing two pressure canisters and integrating the pressure canisters together by welding. However, this method requires high accuracy of welding, thus increasing the cost.
The present invention has been made to solve the aforementioned problems and an object of the present invention is to provide an airbag inflator which is suitable for reducing the manufacturing cost and the weight.
It is also an object of the present invention to provide a method of manufacturing such inflator.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To solve the aforementioned problems, the present invention provides an airbag inflator for generating gas for deploying an airbag comprising a cylindrical body which is divided into a plurality of combustion chambers by at least one inner partition. The portions of the cylindrical body corresponding to the outer peripheral edges of the partition are processed by crimping, and the seal between the outer periphery of the partition and the inside of the cylindrical body is ensured by enlarging the diameter of the partition. The enlargement of the diameter of the partition is achieved by coining for forming a groove in at least one of side surfaces of the partition near the outer periphery thereof.
While such an inflator can be manufactured by relatively easy processing, the seal at the partition can be ensured and the fixing strength between the partition and the body can be further improved. The groove formed by the coining may have a ring shape, a cross shape, or a radial shape.
In a method of manufacturing an airbag inflator of the present invention, an inflator for generating gas for deploying an airbag is manufactured. The method comprises dividing the inside of a cylindrical body into a plurality of combustion chambers by a partition, crimping portions of the cylindrical body corresponding to the outer peripheral edges of the partition, and ensuring the seal between the outer periphery of the partition and the inside of the cylindrical body by enlarging the diameter of the partition. The enlargement of the diameter of the partition is achieved by coining for forming a groove in at least in one of side surfaces of the partition near the outer periphery thereof. In the method of manufacturing the airbag inflator of the present invention, it is preferable that the coining is conducted after the crimping.